Each cell of a battery stores electrical energy as chemical energy in two electrodes, a reductant (anode) and an oxidant (cathode), separated by an electrolyte that transfers the ionic component of the chemical reaction inside the cell and forces the electronic component outside the battery. The output on discharge is an external electronic current I at a voltage V for a time Δt. The chemical reaction of a rechargeable battery must be reversible on the application of a charging I and V. Critical parameters of a rechargeable battery are safety, density of energy that can be stored at a specific power input and retrieved at a specific power output, cycle and shelf life, storage efficiency, and cost of fabrication. Conventional ambient-temperature rechargeable batteries have solid electrodes and a liquid electrolyte. The positive electrode (cathode) consists of a host framework into which the mobile (working) cation is inserted reversibly over a finite solid–solution range. The solid–solution range, which is...

The Li-ion rechargeable battery: a perspective.

Sustainable hydrogen production is an essential prerequisite of a future hydrogen economy. Water electrolysis driven by renewable resource-derived electricity and direct solar-to-hydrogen conversion based on photochemical and photoelectrochemical water splitting are promising pathways for sustainable hydrogen production. All these techniques require, among many things, highly active noble metal-free hydrogen evolution catalysts to make the water splitting process more energy-efficient and economical. In this review, we highlight the recent research efforts toward the synthesis of noble metal-free electrocatalysts, especially at the nanoscale, and their catalytic properties for the hydrogen evolution reaction (HER). We review several important kinds of heterogeneous non-precious metal electrocatalysts, including metal sulfides, metal selenides, metal carbides, metal nitrides, metal phosphides, and heteroatom-doped nanocarbons. In the discussion, emphasis is given to the synthetic methods of these HER electrocatalysts, the strategies of performance improvement, and the structure/composition-catalytic activity relationship. We also summarize some important examples showing that non-Pt HER electrocatalysts could serve as efficient cocatalysts for promoting direct solar-to-hydrogen conversion in both photochemical and photoelectrochemical water splitting systems, when combined with suitable semiconductor photocatalysts.

Noble metal-free hydrogen evolution catalysts for water splitting

Research Development on Sodium-Ion Batteries

The prohibitive cost of platinum for catalyzing the cathodic oxygen reduction reaction (ORR) has hampered the widespread use of polymer electrolyte fuel cells. We describe a family of non-precious metal catalysts that approach the performance of platinum-based systems at a cost sustainable for high-power fuel cell applications, possibly including automotive power. The approach uses polyaniline as a precursor to a carbon-nitrogen template for high-temperature synthesis of catalysts incorporating iron and cobalt. The most active materials in the group catalyze the ORR at potentials within ~60 millivolts of that delivered by state-of-the-art carbon-supported platinum, combining their high activity with remarkable performance stability for non-precious metal catalysts (700 hours at a fuel cell voltage of 0.4 volts) as well as excellent four-electron selectivity (hydrogen peroxide yield <1.0%).

/pdf/high-performance-electrocatalysts-for-oxygen-reduction-3w5qtsq9yn.pdf

High-Performance Electrocatalysts for Oxygen Reduction Derived from Polyaniline, Iron, and Cobalt

Climate change 2014 - Synthesis Report

has been synthesized using sol‐gel and solid‐state methods for 0 < x < 0.5. The electrochemical behavior of the samples was studied in coin‐type cells. When x = 0, the capacity of cells appears at 4.1 V. As x increases, the capacity of the 4.1 V plateau decreases as 1−2x Li per formula unit, and a new plateau at 4.7 V appears. The capacity of the 4.7 V plateau increases as 2x Li per formula unit, so that the total capacity of the samples (both the 4.1 and 4.7 V plateaus) is constant. This is taken as evidence that the oxidation state of Ni in these samples is +2, and therefore they can be written as . The 4.1 V plateau is related to the oxidation of to and the 4.7 V plateau to the oxidation of to . The effect of synthesis temperature, atmosphere, and cooling rate on the structure and electrochemical properties of is also studied on samples made by the sol‐gel method. samples made by heating gels at temperatures below 600°C in air are generally oxygen deficient, leading to Mn oxidation states significantly less than 4. samples heated above 650°C suffer due to disproportionation into with x < 0.5 and with z ≈ 0.2, which occurs above about 650°C. Pure materials can be made by extended heatings near 600°C or by slowly cooling materials heated at higher temperatures. made at 600°C has demonstrated good reversible capacity at 4.7 V in excess of 100 mAh/g for tens of cycles.

Synthesis and Electrochemistry of LiNi x Mn2 − x O 4

Many intermetallic materials deliver poor capacity retention when cycled vs Li Many authors have attributed this poor capacity retention to large volume expansions of the active material Here we report the volume changes of continuous and patterned films of crystalline Al, crystalline Sn, amorphous Si (a-Si), and a-Si 0  6 4 Sn 0  3 6 as they reversibly react with Li measured by in situ atomic force microscopy (AFM) Although these materials all undergo large volume expansions, the amorphous phases undergo reversible shape and volume changes The crystalline materials do not We attribute this difference to the homogeneous expansion and contraction that occurs in the amorphous materials Inhomogeneous expansion occurs in the crystalline materials due to the presence of coexisting phases with different Li concentrations Thin films of a-Si and a-Si 0  6 4 Sn 0  3 6 show good capacity retention with cycle number

https://iopscience.iop.org/article/10.1149/1.1613668/pdf

Reaction of Li with Alloy Thin Films Studied by In Situ AFM

This Review addresses the technical challenges, scientific basis, recent progress, and outlook with respect to the stability and degradation of catalysts for the oxygen evolution reaction (OER) operating at electrolyzer anodes in acidic environments with an emphasis on ion exchange membrane applications. First, the term “catalyst stability” is clarified, as well as current performance targets, major catalyst degradation mechanisms, and their mitigation strategies. Suitable in situ experimental methods are then evaluated to give insight into catalyst degradation and possible pathways to tune OER catalyst stability. Finally, the importance of identifying universal figures of merit for stability is highlighted, leading to a comprehensive accelerated lifetime test that could yield comparable performance data across different laboratories and catalyst types. The aim of this Review is to help disseminate and stress the important relationships between structure, composition, and stability of OER catalysts under different operating conditions.

/pdf/the-stability-challenges-of-oxygen-evolving-catalysts-5bxg0qwy04.pdf

The Stability Challenges of Oxygen Evolving Catalysts: Towards a Common Fundamental Understanding and Mitigation of Catalyst Degradation.

Novel nanostructured material WS2 nanosheets (NSs) were prepared through a simple and highly reproducible approach, namely, a mechanical activation strategy by using WO3 and S as the starting materials, and were explored as electrocatalyst for hydrogen evolution reaction (HER). The as-prepared WS2 NSs reveal separate NSs nanostructure with a sheet thickness of less than 10 nm. On the basis of experimental results obtained under various synthesis conditions, a reasonable reaction process and formation mechanism is proposed, in which the pre-treatment of ball milling is assumed to play a key role for the formation of WS2 NSs. Due to its large active sites originating from its unique structural characteristics such as loosely stacked layers, providing highly exposed rims particularly edges, WS2 NSs catalyst has demonstrated high electrocatalytic activity toward HER, which considerably outperforms the commonly used MoS2 (JDC) catalyst.

WS2 nanosheets as a highly efficient electrocatalyst for hydrogen evolution reaction

We have investigated the impact of electrocatalyst loading on rotating ring-disk electrode (RRDE) experiments for the oxygen reduction reaction on Fe-N-C catalysts (ORR) in acid medium. In particular, the fraction of H 2 O 2 produced as a function of catalyst loading was studied. A dramatic increase in H 2 O 2 release was observed as the catalyst loading was decreased. For the same non-noble metal catalyst (NNMC), the fraction of produced H 2 O 2 varied between less than 5% and greater than 95%, depending on the catalyst loading. These observations suggest that oxygen reduction occurs stepwise, via H 2 O 2 , and if the catalyst is sparsely loaded, the produced H 2 O 2 cannot be efficiently reduced to H 2 O before it escapes. These studies have important implications for fundamental studies of ORR on NNMCs.

Arman Bonakdarpour

Papers

Synthesis and Electrochemistry of LiNi x Mn2 − x O 4

Reaction of Li with Alloy Thin Films Studied by In Situ AFM

The Stability Challenges of Oxygen Evolving Catalysts: Towards a Common Fundamental Understanding and Mitigation of Catalyst Degradation.

WS2 nanosheets as a highly efficient electrocatalyst for hydrogen evolution reaction

Impact of Loading in RRDE Experiments on Fe-N-C Catalysts: Two- or Four-Electron Oxygen Reduction?